The focus of the invention is a novel filament contained within a packaged radiation source device, configured to be a component in an instrumentation application. The specific application and embodiment described is an infrared radiation source for use in various calibration, reference and measurement instruments.
The tradeoffs and requirements of radiation sources for electromagnetic and optical radiation sources, and in particular the use of enclosed electrically-excited filaments, have been the subject of development for many years. As this development addressed more narrow and specific radiation requirements of controlled wavelength emission for accuracy and precision, power efficiency requirements for economy, and loss reduction and temperature control, the problems involved in design and manufacture of suitable radiation sources have become correspondingly more complex.
A particular application environment that has received a great deal of inquiry is the area of infrared radiation, which is efficiently useful and necessary in a variety of measurement and detection instrumentation. Many such applications are limited in power, space and cooling ability and require efficient illumination within a limited spectral band. The difficulty of achieving stability and control of temperature and emission wavelength in a thin, flat, electrically heated radiator has been known. Temperature stability has been a particular development objective of traditional infrared radiation sources for calibration and measurement applications, which rely on steady state heating of an object with relatively large thermal mass. This in turn requires a long turn-on and settling time for stable operation and produces a large amount of waste heat.
U.S. Pat. Nos. 5,838,016 and 6,249,005, both of which are assigned to the assignee of the present invention and are incorporated herein by reference, disclose and claim textured infrared radiation filaments and methods of manufacture. The surface treatment disclosed in said patents enhances the infrared emissions, and the resulting textured infrared radiation filaments compare favorably as an improvement over many previous radiation sources and can usefully replace such traditional reference emission sources.
International patent application number PCT/US98/25771 (WO 99/28729) which is also assigned to the assignee of the present invention and incorporated herein by reference, discloses and claims a radiation source fitted with a concentrating reflector. The reflector is shaped to direct emitted radiation along an axis of the radiation source and through a spectral filter. The reflector is parabolic, although other shapes, such as spherical, conical, and custom contours, can be used.
What is still desired is a radiation source that provides brighter illumination on-axis and a more uniform distribution of far-field illumination. Preferably, the improved radiation source will provide infrared radiation. In addition, the improved radiation source will also preferably include a filament providing infrared emissions enhanced by surface treatment.